Psychobiological approaches have revealed numerous examples of group differences among neuropsychiatric patients with intellectual disabilities. It is unclear, however, to what extent these differences are manifested behaviorally. The focus of this project is the evaluation of individuals with autism, a complex neurodevelopmental disorder that is often accompanied by mental retardation. In the past, methodological difficulties adapting complex psychological paradigms to MR/DD populations have limited investigation. This project proposes to begin the process of overcoming these limitations. In particular, the project seeks to demonstrate the capacity to conduct meaningful evaluations of the behavior of individuals with autism who are severely mentally retarded and have poorly developed language skills. We will apply behavior analytic methods tin a unique way to evaluate specific claims about autistic behavior, comparing severely mentally retarded persons with and without autism. Within both the visual and auditory modalities, we will assess learning and generalization of simple and conditional discriminations, formation of equivalence classes both within and across modalities, immediate and delayed recall, and several other behavioral measures. We have adapted stimulus control procedures developed in our laboratory to assemble a test battery to assess the specificity of cognitive deficits in individuals with autism. We will test whether or not autistic individuals display comparatively more (I) perserveration and behavioral rigidity, (ii) restricted stimulus control (ovcrselective attention), (iii) memory deficits, and (iv) symbolic processing abnormalities. This undertaking will provide an initial attempt to determine whether diagnosis must be considered when designing teaching interventions for individuals in the low range of intellectual function. It can be seen as a first step in developing a more comprehensive neurobehavioral assessment battery for this population.